Carbon nanotubes (hereinafter also referred to as “CNTs”) are one-dimensional nanomaterials composed only of carbon atoms and having a diameter of from 0.4 nm to 50 nm and a length of roughly from 1 μm to hundreds of micrometers. The chemical structure of a carbon nanotube is represented by rolling up and joining a graphite layer. In the case of a carbon nanotube having just one of these layers, the carbon nanotube is referred to as a single-walled carbon nanotube.
Single-walled CNTs are expected to have a wide range of applications as substance and energy stores, separation membranes, electrode materials, and so forth due to their relatively large specific surface area. PTL 1 describes CNTs that have open ends. Open-ended CNTs such as described in PTL 1 have a large specific surface area compared to CNTs that have closed ends.
PTL 2 describes a technique for increasing the specific surface area of single-walled CNTs by carrying out opening formation treatment in which holes are opened at the ends or in the side walls of the single-walled CNTs by oxidation.